The cellular basis of the cutaneous basophil reaction is being examined with the use of mitogens and specific antisera. The mitogens are being studied to determine whether their ability to stimulate T or B cells correlates with their ability to elicit a basophil response. Specific rabbit antisera for guinea pig T and B cells have been prepared and will be used to provide uniform populations of cells to study the passive transfer of this phenomenon. By suitable separation techniques, we are proceeding to establish whether macrophages are the cells responsible for ease or difficulty of tolerance induction to bovine gamma-globulin in various strains of mice. Isolated purified macrophage preparations will be studied for their ability to filter the immunogenic portion of the antigen and transfer responsiveness. The genetics of this trait are being studied by breeding F1 to parent backcrosses and studying their responsiveness to this antigen.